JP2965443B2 - Separation method of specific gas from mixed gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas separation system that uses a gas separation membrane module to select and extract a specific gas from a mixed gas.

[0002]

2. Description of the Related Art There are various methods for separating or removing gas. For example, as a typical example of separating oxygen, nitrogen, etc. from air, a cryogenic air separation method or a recent small-to-medium scale separation method is used. There is a rapidly increasing adsorption method typified by the PSA method. However, recently, the performance of various polymer membranes that selectively transmit a specific gas from a mixed gas has been improved. Membrane separation methods using these polymer membranes have been vigorously industrialized.

[0003] Membrane separation, for example, does not involve a phase change such as cryogenic separation, and can be separated with little energy consumption.
Further, it is said that there is an advantage that it is extremely easy to reduce the size and weight because it is not separated using a chemical reaction.

FIG. 7 shows a conventional equipment flow using a hollow fiber module as a membrane separation method.

[0005] As shown in FIG. 7, an extremely simple system in which a mixed gas passes through, for example, air, a valve 12, is pressurized by a compressor 11, separated by a hollow fiber module 1, and becomes oxygen and nitrogen. And the equipment configuration.

FIG. 4 is a schematic diagram when oxygen and nitrogen are separated from air using the hollow fiber.

[0007] As shown in FIG.
Since it enters the entrance-side hollow chamber 5 and is partitioned by the partition plate 4,
Air is introduced into the hollow fiber holes 23.

In the actual machine, the hollow fiber holes 23 are constituted by a large number of hollow fibers, for example, 18,000.

The flow rate of the introduced air is about 300 Nm ³ /
Hr. And the pressure is about 20 kg / cm ² G, but oxygen in the permeable air flows through the hollow fiber hole 23 into the body wall chamber 3 as shown in the figure.

As shown schematically, the cross section of the hollow fiber membrane 24 which is a permeable portion is shown in FIG.
And oxygen passes through it, and nitrogen is
Separation is performed using the property that does not pass through.

Therefore, when air is continuously supplied at a high pressure, oxygen, which is a permeated gas, is taken out from the body wall chamber 3 and, as shown in FIG. In the present example, if the measured value is within a specified value range, that is, in terms of the oxygen concentration, if it is 90%, it is taken out as a product.

On the other hand, the gas component which is not permeated, that is, nitrogen which is not permeated gas, flows through the hollow fiber hole 23 in FIG. After passing through 16, it is discharged to the atmosphere.

Therefore, the above operation is continuously performed, and
FIG. 2 shows data obtained by measuring the flow rate of oxygen as a permeated gas over 0 days.

In this case, the material of the hollow fiber is a polysulfone having an inner diameter of 0.5 mm and an outer diameter of 1.0 mm.

As can be seen from FIG. 2, according to the conventional method, the amount of oxygen obtained gradually decreases one to two days after start-up.

[0016] Then, after about 10 days, only about half of the amount at the time of start-up can be obtained, and this is a very serious problem.

When the cause was investigated and analyzed from a macro and micro standpoint, as shown in FIG. 6, when a mixed gas was passed for a certain period of time, nitrogen, which is a non-permeated gas component, was gradually called a decomposition active layer. It was found that it adhered to the inner surface layer of the hollow fiber membrane 24 and penetrated into the inner surface part of the hollow fiber membrane porous portion 25, which inhibited oxygen permeation.

It has been found that the nitrogen adhering increases in proportion to the number of operating days, indicating the decrease in the amount of oxygen described above.

Therefore, the amount of oxygen decreases with the passage of time, and furthermore, the attached nitrogen component permeates, and the mixing ratio with the oxygen component gradually increases, and the quality falls significantly below the specified value of the product. I was

On the other hand, as an invention for improving the separation efficiency of a membrane separation system, JP-A-2-90914 can be found.

In this embodiment, pressurization and depressurization are alternately performed in order to further improve the separation performance. This is different from the present invention, which is a viewpoint of removing components adhering to the membrane.
The above problem cannot be solved.

[0022]

As described above, when gas separation is performed in a membrane separation system, from the start-up, if used continuously, a large decrease in the amount of permeated gas and impurities in the permeated gas will occur. Is increased with time.

In addition, there are the following additional problems.

That is, (1) The porous portion of the hollow fiber membrane is made of, for example, nitrogen,
Clogging is caused by argon, moisture, and poisoning components. The performance of the film is greatly reduced, the deterioration is accelerated, and the life is extremely shortened.

(2) Due to the clogging, it is necessary to gradually increase the pressure of the mixed gas, which significantly reduces the strength of the film, causes the film to yield, and eventually breaks. And cause a leak.

(3) In the case of a hollow fiber membrane, the number is about 10
Since it is composed of a large number of membranes, such as 000, and its binding part is hardened with resin, repair is almost impossible. Was extremely difficult.

[0027]

According to the present invention, a raw material mixed gas is pressurized, then introduced into a gas separation membrane module, and a specific gas in the mixed gas is passed through the gas separation membrane module. In the method for separating the specific gas, continuously measure the amount of gas permeated by the gas separation membrane module, when the gas amount is less than a preset permeate gas amount, switch the raw material mixed gas flow, A method for separating a specific gas from a mixed gas, which comprises heating the mixture to a predetermined temperature and then introducing the gas separation membrane module from the outlet side thereof to remove non-permeated components attached to the separation membrane.

[0028]

[Action]

(1) When a poisoning component or a component not expected to permeate adheres to the inner surface of the porous portion of the hollow fiber membrane, that is, the active separation layer, the gas component is automatically detected and the flow of the mixed gas is reversed at an early stage. By doing so, the components adhering to the active separation layer of the hollow fiber according to the amount of adhesion can be removed.

(2) Therefore, the amount of permeated gas and its components are appropriately monitored, and based on the data, the flow of the raw material mixed gas is automatically switched, and the removal capacity according to the amount of adhering gas is automatically adjusted. As a result, the temperature of the mixed gas was controlled so that the component of the permeated gas could be automatically set to a specified value even when the component of the raw material mixed gas fluctuated.

[0030]

FIG. 1 shows an embodiment of the present invention.

That is, the air as the raw material mixed gas is supplied by the compressor 11 at a flow rate of 300 Nm ³ / Hr. Is
With the pressure increased from 1.5 kg / cm ² G to about 20 kg / cm ² G, the valve 12 is first opened and the valve 13 is operated closed, so that the pressurized air enters the valve 12 and From the mixed gas inlet 7, the hollow fiber module 1
to go into.

From the mixed gas inlet 7, first, the inlet hollow chamber 5
The air enters the hollow fiber holes 23 shown in FIG. 4 because the hollow chamber is partitioned by the partition plate 4.

Then, oxygen in the air which is easily permeated passes through the hollow fiber membrane porous portion 25 of the hollow fiber membrane 24, passes through the body side chamber 3, and is taken out at the body side chamber gas outlet 9.

The pressure of the permeated oxygen was about 2 kg / cm ² G due to pressure loss due to permeation.

Further, the amount of oxygen and the oxygen concentration were measured by a gas detector 19 via a valve 18.

As a result, as shown in FIG. 2, the flow rate of the permeated gas one day after the start-up is about 55 Nm ³ / H.
r. Met.

The oxygen concentration was about 93%, which was higher than the specified value.

Next, when continuously operating in this state,
After 1.5 days, the flow rate of the permeated gas began to gradually decrease, and as shown in FIG. 2, was about 50 Nm ³ / Hr. Became.

As shown in FIG. 4, the nitrogen gas flows through the hollow fiber holes 23, enters the outlet hollow chamber 6, and passes through the hollow chamber gas outlet 10 shown in FIG. Since the valve 16 is open "at this time, the valve 15 is closed", the gas is discharged to the outside through the non-permeate gas line.

At this time, the pressure of nitrogen was about 18 kg / cm ² G, since the pressure loss was extremely small due to non-permeation.

When about 1.5 days have passed, the permeated gas amount began to drop below the specified value and deviated from the set value of the gas detector 19, so that the valve 12 was closed by the programmed control system. On the contrary, the normally closed valve 13 is opened, and the mixed gas flows into the line of the valve 13 and is heated to about 30 ° C. by the heater 14.
The temperature is increased, and enters the hollow fiber module 1 through the mixed gas reverse flow inlet 8.

Next, as shown in FIG. 5, the air heated to about 30 ° C. enters the body side chamber 3, and oxygen in the air passes through the hollow fiber membrane porous portion 25 of the hollow fiber membrane 24. Hollow fiber hole 23
to go into.

At this time, poisonous components such as nitrogen adhered in the previous step accompany the gas, that is, the gap between the porous portions is widened by heating, and the peeling phenomenon of the adhered components occurs due to the back pressure. Almost 100% of the adhered components can be removed,
It was determined by detecting the permeated gas.

As a result, in the solid line of the present invention shown in FIG. 2, as in the case of (gas heating), the initial permeated gas amount was about 55 Nm.
³ / Hr. Was able to secure.

In this embodiment, the lower limit of the gas permeation flow rate is set to 6
Until the day, 50 Nm ³ / Hr. And 50 Nm ³ / Hr.
, It was found that the gas flow was automatically switched, the corresponding heater capacity was set, the temperature of the mixed gas was increased, and the mixture was automatically controlled.

Further, after 6 days, the lower limit of the permeated gas amount is set to 48 Nm ³ / Hr. As a result, good results were obtained as shown in FIG.

On the other hand, the nitrogen at the time of the backflow is explained with reference to FIG.
Since nitrogen is not permeated, the nitrogen is discharged from the body side chamber gas outlet 9 in FIG. 1 and is discharged as a non-permeated gas through a valve 17 which is opened from a closed state. At that time, the valve 18 is changed from open to closed.

Further, apart from the above, according to the present invention, when the mixed gas is caused to flow backward, an operation in which the temperature of the mixed gas is not increased by the heater 14 is executed.
As shown by the "(gas non-heated)" line in the solid line shown in FIG. 2, the permeated gas amount was larger than that of the conventional method, but was less than in the case of gas heating.

As a second embodiment of the present invention, a method for separating carbon dioxide, methane and the like from natural gas was implemented.

In this case, the nature of the natural gas is about 72 ° C.
The gas components were 71% CO ₂ , 25% methane, 3% nitrogen, and 1% moisture. Natural gas flow is about 150N
m ³ / Hr. It is.

As the material of the hollow fiber, unlike the case of the air, since the temperature of the gas to be treated is as high as 72 ° C., a heat-resistant polyimide material is used. The outer diameter is 6 mm, and the number of hollow fibers is about 10,600.

Under these conditions, continuous operation was performed for 10 days using the same apparatus as in the above embodiment. The results are shown in FIG.

The dashed line “× −− ×” in FIG. 3 shows the time-dependent change data of the flow rate of the carbon dioxide gas as the permeated gas in the case of the conventional method. As can be seen from FIG. As time passes, methane, nitrogen, moisture, etc., which are components that are difficult to permeate, begin to adhere to the separation active layer of the hollow fiber,
With the passage of time on the second and third days, the flow rate of the carbon dioxide gas gradually decreased. After 10 days, only about half of the initial flow rate of the carbon dioxide gas was obtained.

Next, an experiment was conducted with the system of the present invention as shown in Example 1 above. At that time, the temperature of the gas was raised by about 30 ° C., and as a result, a thick solid line “—” in FIG. like,
When the backflow was performed every other day, the methane, nitrogen, hydrogen and the like adhering to the separation active layer of the hollow fiber were easily separated, and the initial highest level of separation performance could be maintained.

Further, FIG. 3 shows the results of an attempt to execute the case of reverse flow but no gas heating in the system of the present invention.
As indicated by the thin line "△-△", the flow rate of the permeated gas, carbon dioxide, gradually decreases over time and is not heated because the adhered components do not peel off sufficiently and accumulate because they are not heated. It can be said that the gas separation performance is less deteriorated than the conventional method, and it was impossible to maintain the initially highest level of separation performance.

As is clear from the above Examples 1 and 2, it is clear that heating the air, exhaust gas and the like flowing at the time of backflow widens the gaps between the porous portions of the hollow fiber and causes a phenomenon of separation of the components attached to the porous portions. It became.

The heating temperature in this case may be about 30 ° C. or higher than the temperature of the raw material gas to be treated.
When the temperature is lower than 0 ° C., the backflow effect is small because the space between the porous portions is not widened, which is not preferable.

The upper limit of the temperature may be appropriately set based on the heat-resistant temperature of the hollow fiber, the capacity of the heater heating source, and the like.

In this embodiment, a hollow fiber is used as an example of the gas separation membrane module. However, the present invention is not limited to this, and may be, for example, a spiral type, a plate and fin type, or the like. In this case, the same functions and effects are achieved.

[0060]

As described above, according to the gas separation system of the present invention, (1) the permeated gas flow rate and the permeated gas concentration can be continuously operated while maintaining the initial maximum levels.

(2) Clogging and deterioration of the film due to poisoning components were extremely small, and a long life could be secured.

(3) According to the above item (2), it is not necessary to increase the pressure of the compressor, and extremely stable operation can be performed.

(4) With the above effects, maintenance-free operation can be performed comprehensively, and total cost reduction can be established.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a system example of the present invention.

FIG. 2 is an explanatory diagram (an example of performance test data) showing a change with time of a hollow fiber permeated gas flow rate by the system of the present invention and the system of the conventional method.

FIG. 3 is an explanatory diagram (an example of performance test data) showing the change over time in the flow rate of a hollow fiber permeable gas by the system of the present invention and the system of the conventional method.

FIG. 4 is an explanatory diagram showing an example of initial transmission behavior of the present invention and a conventional method.

FIG. 5 is an explanatory view showing an example of a backflow permeation behavior after aging according to the present invention.

FIG. 6 is an explanatory diagram showing an example of a permeation behavior after aging according to a conventional method.

FIG. 7 is an explanatory diagram showing a system example of a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hollow fiber module 2 Hollow fiber 3 Body side chamber 4 Partition plate 5 Inlet side hollow chamber 6 Outlet side hollow chamber 7 Mixed gas inlet 8 Mixed gas reverse flow inlet 9 Body side chamber gas outlet 10 Hollow chamber gas outlet 11 Compressor 12 Valve 13 Valve 14 Heater 15 Valve 16 Valve 17 Valve 18 Valve 19 Gas detector 20 Heater heating source 21 Thermometer 22 Control valve 23 Hollow fiber hole 24 Hollow fiber membrane 25 Hollow fiber membrane porous part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01D 53/22

Claims (1)

(57) [Claims] 1. A method for separating a specific gas from a mixed gas by pressurizing a raw material mixed gas, introducing the mixed gas into a gas separation membrane module, allowing a specific gas in the mixed gas to pass through the gas separation membrane module, The amount of gas permeated by the gas separation membrane module is continuously measured, and when the amount of gas is smaller than a preset amount of permeated gas, the raw material mixed gas flow is switched and heated to a predetermined temperature. A method for separating a specific gas from a mixed gas, wherein the method is introduced from an outlet side of the gas separation membrane module to remove non-permeated components attached to the separation membrane.